Preparation of copper-rich copper indium (gallium) diselenide/disulfide nanoparticles

A method for preparing copper-rich CIGS nanoparticles having the general formula CuxInyGazSaSeb, wherein y+z=1, a+b=2, and x>y+z, the method comprising:

• heating a copper salt together with at least one salt selected from the group consisting of indium salts and gallium salts in a solvent at a first temperature to produce a reaction solution;
• adding an organo-chalcogen precursor to the reaction solution;
• heating the reaction solution to a second temperature while stirring for a first time interval;
• cooling the reaction solution to a third temperature, the third temperature being between the second temperature and room temperature;
• stirring the reaction solution for a second time interval at the third temperature to anneal the reaction solution, the second time interval being between about 4 hours and about 24 hours;
• cooling the reaction solution from the third temperature to room temperature;
• and
• isolating nanoparticles from the reaction solution.